ffmpeg/libavcodec/xface.h

   1 /*
   2  * Copyright (c) 1990 James Ashton - Sydney University
   3  * Copyright (c) 2012 Stefano Sabatini
   4  *
   5  * This file is part of FFmpeg.
   6  *
   7  * FFmpeg is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU Lesser General Public
   9  * License as published by the Free Software Foundation; either
  10  * version 2.1 of the License, or (at your option) any later version.
  11  *
  12  * FFmpeg is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Lesser General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Lesser General Public
  18  * License along with FFmpeg; if not, write to the Free Software
  19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20  */
  21
  22 /**
  23  * @file
  24  * X-Face common definitions.
  25  */
  26
  27 #include <stdint.h>
  28
  29 /* define the face size - 48x48x1 */
  30 #define XFACE_WIDTH  48
  31 #define XFACE_HEIGHT 48
  32 #define XFACE_PIXELS (XFACE_WIDTH * XFACE_HEIGHT)
  33
  34 /* compressed output uses the full range of printable characters.
  35  * In ASCII these are in a contiguous block so we just need to know
  36  * the first and last. The total number of printables is needed too. */
  37 #define XFACE_FIRST_PRINT '!'
  38 #define XFACE_LAST_PRINT '~'
  39 #define XFACE_PRINTS (XFACE_LAST_PRINT - XFACE_FIRST_PRINT + 1)
  40
  41 /*
  42  * Image is encoded as a big integer, using characters from '~' to
  43  * '!', for a total of 92 symbols. In order to express 48x48=2304
  44  * bits, we need a total of 354 digits, as given by:
  45  * ceil(lg_92(2^2304)) = 354
  46  */
  47 #define XFACE_MAX_DIGITS 354
  48
  49 #define XFACE_BITSPERWORD 8
  50 #define XFACE_WORDCARRY (1 << XFACE_BITSPERWORD)
  51 #define XFACE_WORDMASK (XFACE_WORDCARRY - 1)
  52
  53 #define XFACE_MAX_WORDS ((XFACE_PIXELS * 2 + XFACE_BITSPERWORD - 1) / XFACE_BITSPERWORD)
  54
  55 /* Portable, very large unsigned integer arithmetic is needed.
  56  * Implementation uses arrays of WORDs. */
  57 typedef struct {
  58     int nb_words;
  59     uint8_t words[XFACE_MAX_WORDS];
  60 } BigInt;
  61
  62 /**
  63  * Add a to b storing the result in b.
  64  */
  65 void ff_big_add(BigInt *b, uint8_t a);
  66
  67 /**
  68  * Divide b by a storing the result in b and the remainder in the word
  69  * pointed to by r.
  70  */
  71 void ff_big_div(BigInt *b, uint8_t a, uint8_t *r);
  72
  73 /**
  74  * Multiply a by b storing the result in b.
  75  */
  76 void ff_big_mul(BigInt *b, uint8_t a);
  77
  78 /* Each face is encoded using 9 octrees of 16x16 each. Each level of the
  79  * trees has varying probabilities of being white, grey or black.
  80  * The table below is based on sampling many faces */
  81 enum XFaceColor { XFACE_COLOR_BLACK = 0, XFACE_COLOR_GREY, XFACE_COLOR_WHITE };
  82
  83 /* Data of varying probabilities are encoded by a value in the range 0 - 255.
  84  * The probability of the data determines the range of possible encodings.
  85  * Offset gives the first possible encoding of the range. */
  86 typedef struct {
  87     int range;
  88     int offset;
  89 } ProbRange;
  90
  91 extern const ProbRange ff_xface_probranges_per_level[4][3];
  92
  93 extern const ProbRange ff_xface_probranges_2x2[16];
  94
  95 void ff_xface_generate_face(uint8_t *dst, uint8_t * const src);